The present invention relates to a new and distinctive tomato mutant allele, designated “PSAF” for Peotec Seeds allflesh. There are numerous steps in the development of any novel, desirable plant germplasm. Plant breeding begins with the analysis and definition of problems and weaknesses of the current germplasm, the establishment of program goals, and the definition of specific breeding objectives. The next step is selection of germplasm that possess the traits to meet the program goals. The goal is to combine in a single variety or hybrid an improved combination of desirable traits from the parental germplasm. These important traits may include higher yield, field performance, fruit and agronomic quality such as firmness, color, content in soluble solids, acidity and viscosity, resistance to diseases and insects, and tolerance to drought and heat. With mechanical harvesting of the tomato fruits for process purpose, i.e. juice, paste, catsup, etc, uniformity of plant characteristics such as germination, growth rate, maturity and plant uniformity is also important.
Practically speaking, all cultivated and commercial forms of tomato belong to a species most frequently referred to as Lycopersicon esculentum Miller. Lycopersicon is a relatively small genus within the extremely large and diverse family Solanaceae which is considered to consist of around 90 genera, including pepper, tobacco and eggplant. The genus Lycopersicon has been divided into two subgenera, the esculentum complex which contains those species that can easily be crossed with the commercial tomato and the peruvianum complex which contains those species which are crossed with considerable difficulty (Stevens, M., and Rick, C. M. 1986. Genetics and Breeding. In: The Tomato Crop. A scientific basis for improvement, pp. 35-109. Atherton, J., Rudich, G. (eds.). Chapman and Hall, New York). Due to its value as a crop, L. esculentum Miller has become widely disseminated all over the world. Even if the precise origin of the cultivated tomato is still somewhat unclear, it seems to come form the Americas, being native to Ecuador, Peru and the Galapagos Island and initially cultivated by Aztecs and Incas as early as 700 AD. Mexico appears to have been the site of domestication and the source of the earliest introduction. It is supposed that the cherry tomato, L. esculentum var. cerasiforme, is the direct ancestor of modem cultivated forms.
Tomato is grown for its fruit, widely used as a fresh market or processed product. As a crop, tomato is grown commercially wherever environmental conditions permit the production of an economically viable yield. In California, the first largest process market and second largest fresh market in the United States, processing tomato are harvested by machine. The majority of fresh market tomatoes are harvested by hand at vine ripe and mature green stage of ripeness. Fresh market tomatoes are available in the United States year round. Process tomato season in California is from late June to September. Process tomato are used in many forms, as canned tomatoes, tomato juice, tomato sauce, puree, paste or even catsup. Over the 500,000 acres of tomatoes that are grown annually in the US, approximately 40% are grown for fresh market consumption, the balance are grown for processing.
Tomato is a simple diploid species with twelve pairs of differentiated chromosomes. The cultivated tomato is self fertile and almost exclusively self-pollinating. The tomato flowers are hermaphrodites. Commercial cultivars were initially open pollinated. Most have now been replaced by better yielding hybrids. Due to its wide dissemination and high value, tomato has been intensively bred. This explains why such a wide array of tomato are now available. The shape may range from small to large, and there are cherry, plum, pear, standard, and beefsteak types. Tomatoes may be grouped by the amount of time it takes for the plants to mature fruit for harvest and, in general the cultivars are considered to be early, midseason or late-maturing.
Tomatoes can also be grouped by the plant's growth habit; determinate or indeterminate. Determinate plants tend to grow their foliage first, then set flowers that mature into fruit if pollination is successful. All of the fruit tend to ripen on a plant at about the same time. Indeterminate tomatoes start out by growing some foliage, then continue to produce foliage and flowers throughout the growing season. These plants will tend to have tomato fruit in different stages of maturity at any given time. More recent developments in tomato breeding have led to a wider array of fruit color. In addition to the standard red ripe color, tomatoes can be creamy white, lime green, pink, yellow, golden, or orange.
Choice of breeding or selection methods depends on the mode of plant reproduction, the heritability of the trait(s) being improved, and the type of cultivar used commercially (e.g., F1 hybrid cultivar, pureline cultivar, etc.). For highly heritable traits, a choice of superior individual plants evaluated at a single location will be effective, whereas for traits with low heritability, selection should be based on mean values obtained from replicated evaluations of families of related plants. Popular selection methods commonly include pedigree selection, modified pedigree selection, mass selection, and recurrent selection.
The complexity of inheritance influences choice of the breeding method. Backcross breeding is used to transfer one or a few favorable genes for a highly heritable trait into a desirable cultivar. This approach has been used extensively for breeding disease-resistant cultivars. Various recurrent selection techniques are used to improve quantitatively inherited traits controlled by numerous genes. The use of recurrent selection in self-pollinating crops depends on the ease of pollination, the frequency of successful hybrids from each pollination, and the number of hybrid offspring from each successful cross.
Each breeding program should include a periodic, objective evaluation of the efficiency of the breeding procedure. Evaluation criteria vary depending on the goal and objectives, but should include gain from selection per year based on comparisons to an appropriate standard, overall value of the advanced breeding lines, and number of successful cultivars produced per unit of input (e.g., per year, per dollar expended, etc.).
Promising advanced breeding lines are thoroughly tested and compared to appropriate standards in environments representative of the commercial target area(s) for three years at least. The best lines are candidates for new commercial cultivars; those still deficient in a few traits are used as parents to produce new populations for further selection.
These processes, which lead to the final step of marketing and distribution, usually take from eight to 12 years from the time the first cross is made. Therefore, development of new cultivars is a time-consuming process that requires precise forward planning, efficient use of resources, and a minimum of changes in direction.
A most difficult task is the identification of individuals that are genetically superior, because for most traits the true genotypic value is masked by other confounding plant traits or environmental factors. One method of identifying a superior plant is to observe its performance relative to other experimental plants and to a widely grown standard cultivar. If a single observation is inconclusive, replicated observations provide a better estimate of its genetic worth.
The goal of plant breeding is to develop new, unique and superior tomato inbreds and hybrids. The breeder initially selects and crosses two or more parental lines, followed by repeated selfing and selection, producing many new genetic combinations. The breeder can theoretically generate billions of different genetic combinations via crossing, selfing and mutations. The breeder has no direct control at the cellular level. Therefore, two breeders will never develop the same line, or even very similar lines, having the same tomato traits.
Each year, the plant breeder selects the germplasm to advance to the next generation. This germplasm is grown under unique and different geographical, climatic and soil conditions, and further selections are then made, during and at the end of the growing season. The varieties which are developed are unpredictable. This unpredictability is because the breeder's selection occurs in unique environments, with no control at the DNA level (using conventional breeding procedures), and with millions of different possible genetic combinations being generated. A breeder of ordinary skill in the art cannot predict the final resulting lines he develops, except possibly in a very gross and general fashion. The same breeder cannot produce the same line twice by using the exact same original parents and the same selection techniques. This unpredictability results in the expenditure of large research monies to develop a superior new tomato varieties.
The development of commercial tomato hybrids requires the development of homozygous inbred lines, the crossing of these lines, and the evaluation of the crosses. Pedigree, backcross or recurrent selection breeding methods are used to develop lines from breeding populations. Breeding programs combine desirable traits from two or more lines or various broad-based sources into breeding pools from which mutant alleles are developed by selfing and selection of desired phenotypes. The new inbreds are crossed with other inbred lines and the hybrids from these crosses are evaluated to determine which have commercial potential.
Pedigree breeding is used commonly for the improvement of self-pollinating crops or inbred parents of cross-pollinating crops. Two parents which possess favorable, complementary traits are crossed to produce an F1. An F2 population is produced by selfing one or several F1′s or by intercrossing two F1′s (sib mating). Selection of the best individuals is usually begun in the F2 population; then, beginning in the F3, the best individuals in the best families are selected. Replicated testing of families, or hybrid combinations involving individuals of these families, often follows in the F4 generation to improve the effectiveness of selection for traits with low heritability. At an advanced stage of inbreeding (i.e., F6 and F7), the best lines or mixtures of phenotypically similar lines are tested for potential release as new cultivars or new parents for hybrids.
Mass and recurrent selections can be used to improve populations of either self- or cross-pollinating crops. A genetically variable population of heterozygous individuals is either identified or created by intercrossing several different parents. The best plants are selected based on individual superiority, outstanding progeny, or excellent combining ability. The selected plants are intercrossed to produce a new population in which further cycles of selection are continued.
Backcross breeding has been used to transfer genes for a simply inherited, highly heritable trait into a desirable homozygous cultivar or inbred which is the recurrent parent. The source of the trait to be transferred is called the donor parent. The resulting plant is expected to have the attributes of the recurrent parent (e.g., cultivar) and the desirable trait transferred from the donor parent. After the initial cross, individuals possessing the phenotype of the donor parent are selected and repeatedly crossed (backcrossed) to the recurrent parent. The resulting plant is expected to have the attributes of the recurrent parent (e.g., cultivar) and the desirable trait transferred from the donor parent.
Descriptions of other breeding methods that are commonly used for different traits and crops can be found in one of several reference books (e.g., “Principles of Plant Breeding” John Wiley and Son, pp. 115-161, 1960; Allard, 1960; Simmonds, 1979; Sneep et al., 1979; Fehr, 1987).
Proper testing should detect any major faults and establish the level of superiority or improvement over current cultivars. In addition to showing superior performance, there must be a demand for a new cultivar that is compatible with industry standards or which creates a new market. The introduction of a new cultivar will incur additional costs to the seed producer, the grower, processor and consumer; for special advertising and marketing, altered seed and commercial production practices, and new product utilization. The testing preceding release of a new cultivar should take into consideration research and development costs as well as technical superiority of the final cultivar. For seed-propagated cultivars, it must be feasible to produce seed easily and economically.
Once the inbreds that give the best hybrid performance have been identified, the hybrid seed can be reproduced indefinitely as long as the homogeneity of the inbred parent is maintained. A single-cross hybrid is produced when two inbreds are crossed to produce the F1 progeny.
Tomato is an important and valuable field crop. Thus, a continuing goal of plant breeders is to develop stable, high yielding tomato hybrids that are agronomically sound. The reasons for this goal are obviously to maximize the amount of fruit produced on the land used as well as to improve the fruit qualities. To accomplish this goal, the tomato breeder must select and develop tomato plants that have the traits that result in superior parental lines for producing hybrids.
According to the invention, there is provided a novel mutant allele, designated “PSAF”. This invention thus relates to a tomato seed, a tomato plant, a tomato variety, a tomato hybrid and to a method of producing a tomato plant. More specifically, the invention relates to a mutant allele designated PSAF which when present as a homozygous recessive produces a tomato fruit having solid cavity areas and lacking the gel or liquid which is present in the cavities of normal tomato fruits.
Another aspect of the invention relates to any tomato seed or plant having the mutant allele PSAF.
In another aspect, the present invention provides regenerable cells for use in tissue culture. The tissue culture will preferably be capable of regenerating plants having the physiological and morphological characteristics of the foregoing inbred tomato plant, and of regenerating plants having substantially the same genotype as the foregoing inbred tomato plant. Preferably, the regenerable cells in such tissue cultures will be embryos, protoplasts, meristematic cells, callus, pollen, leaves, anthers, stems, petioles, roots, root tips, fruits, seeds, flowers, cotyledons, hypocotyls or the like. Still further, the present invention provides tomato plants regenerated from the tissue cultures of the invention.
Another objective of the invention is to provide methods for producing other inbred tomato plants derived from a tomato plant having the PSAF allele. Tomato lines derived by the use of those methods are also part of the invention.
The invention also relates to methods for producing a tomato plant containing in its genetic material one or more transgenes and to the transgenic tomato plant produced by that method.
The invention further provides methods for developing tomato plant in a tomato plant breeding program using plant breeding technique including recurrent selection, backcrossing, pedigree breeding, restriction fragment length polymorphism enhanced selection, genetic marker enhanced selection and transformation. Seeds, tomato plant, and parties thereof produced by such breeding methods are also part of the invention.